The
top-level domain indicates the type of institution sponsoring
a site, so it can give searchers valuable information about the
kind of site they are visiting. Some of the most common are as
follows:

.edu
- educational institution Sites with this domain are generally among
the best for finding high quality material for academic papers.
But keep in mind that many faculty members put syllabi on the
Web, and students create Web pages to meet course requirements,
so not all sites with an .edu domain will be useful for academic
research.

.gov
- federal governmentMany government agencies
have Web sites that publish highly reliable information about
legislation; statistics of all sorts, such as census data;
tax forms; medical information, etc. Be aware that information
on the sites of foreign governments may not be so reliable.
For example, a Chinese government site might publish questionable
information about human rights in China.

.org
- non profit organizationThese include, but are
not limited to, organizations that espouse causesand that
use the Web to promote them. They range from highly reliable
to utterly untrustworthy, so users must check "About us"
and other such links on their pages for information about their
philosophy, goals, work, funding, etc.

.com
- commercial entitySites with this domain are created by
companies to advertise and sell their products and to publish
company information for customers, stockholders, and potential
investors. Much of the quality information that users can purchase,
such as access to online publications, have the .com domain.